The membrane ATPase complex (FoFl) of Bacillus stearothermophilus will be isolated by precipitation from solubilized membrane suspensions with antibody prepared from the purified peripheral (Fl) component of the complex. The lipid composition of the isolated FoFl complex will be compared to the total membrane lipid composition and to the composition of lipid depleted (cholate extracted) membrane. The patterns of lipid metabolism in the three preparations will be compared by determining the rates of turnover of the phosphorus, glycerol, and fatty acid moieties of each lipid component. Membranes will be isolated from cells grown or treated under conditions which result in different patterns of metabolism of the total membrane lipid, and different total lipid compositions. The extent and rates of exchange of the lipid associated with the ATPase complex with the bulk membrane lipid will be determined by the fusion of liposomes (labeled with 32P) with lipid depleted membranes (lipid labeled with 3H-glycerol) and by the fusion of stripped (Fl free) membrane (labeled with 32P) with washed membrane (labeled with 3H-glycerol). The Fl specific antibody does not react with stripped membrane. The rates and extent of exchange of the FoFl associated lipid with the bulk lipid will be determined by the # ratio of 3H to 32P in the isolated FoFl fraction.